The present invention pertains to an apparatus for magnifying an image. More particularly, the present invention pertains to a bioptic telescope comprising an eye piece lens, a Schmidt prism, and an objective lens which is mounted to the lens of a pair of eyeglasses.
Low vision patients are patients whose corrected visual acuity in an eye is in the range of 20/100 or worse. Such a patient is capable of distinguishing a letter 61 millimeters high at a distance of 20 feet from the eye of the patient when wearing corrective glasses. Those patients have great difficulty reading signs and distinguishing the shapes of objects, and must wear various low vision aids such as vision-correcting lenses, prisms, and telescopes mounted to the lenses of the eyeglasses. A telescope mounted to the front of an eyeglasses lens is commonly termed a bioptic telescope.
It has now been discovered that a periscope can be mounted behind an eyeglasses lens and used as a low vision aid. The present invention is directed to a bioptic periscope mounted to an eyeglasses lens and behind the lens can be constructed having the same focal length and magnification as a bioptic telescope, but because the light path in a periscope is folded so that there are three internal reflections of the light, a bioptic periscope occupies less space than a bioptic telescope having the same focal length and power of magnification.
Bioptic telescopes small enough to be attached to the lens of a pair of eyeglasses have been known in the art for many years, but most such devices suffer the disadvantage that they must be secured to the front of an eyeglasses lens, and thus extend forward from the eyeglasses lens for a distance of up to four inches. Most such devices are heavy and are immediately noticed by others, so as cosmetically undesirable. Currently available bioptic telescopes are either Galilean or Keplerian telescopes that are generally cylindrical in form and have both objective and eye piece lenses oriented along the axis of a cylinder. Currently available bioptic telescopes range in size from about one to about four inches in length and have magnifying powers ranging from about 2X to about 8X.
Examples of currently available bioptic telescopes used for correction of low vision include various distance telescopes made by manufacturers such as Keeler, Walters, and Selsi which can be purchased through American Low Vision International, P.O. Box 34564, San Antonio, Tex. 78218. Those telescopes are mounted on the outside of an eyeglasses lens. Eyeglasses having telescopes mounted on a lens are used for distance viewing, and with additional front lenses, can be used for near viewing.
Typically, those telescopes are mounted to eyeglasses by boring a hole of appropriate size through the lens either immediately above or below the normal line of sight and securing the telescope within the hole. Both head and eye movements are required to use a bioptic telescope mounted in an eyeglasses lens. Those movements must be practiced until they become automatic and natural for a patient to be successful in using a bioptic telescope. If the telescope is mounted above the line of sight, the patient first rotates the head downwardly to direct the telescope at the object the patient wishes to see, and then the patient rotates the eyes upwardly by a corresponding amount to bring the visual axis of the eye into coincidence with the optical axis of the telescope to visualize an object through the telescope.
One bioptic telescope lens system is comprised of multiple telescopes mounted on a single eyeglasses lens. For example, the "Honey Bee Lens" made by Designs for Vision Laboratory, New York, is used for patients having severely impaired vision. That low vision aid has three small telescopes, each containing thirteen lenses, attached to the exterior of each lens of the eyeglasses. The telescopes are aimed in different directions, and the three images from the three telescopes intersect at the patient's eye to provide a relatively wide field of view. The particular disadvantage of that three telescope system is that it is exceedingly heavy and uncomfortable to wear. Although cushion pads can reduce pressure on the bridge of the nose and on the ears, wearers frequently suffer discomfort and skin maceration due to the unavoidable weight of the eyeglasses frame and its total of six attached telescopes, when the apparatus is constructed for use with both eyes.
Bioptic telescopes mounted to the lenses of eyeglasses are worn by patients having impaired visual actuity so that those patients can pass the visual actuity tests required for operating a motor vehicle. Although a bioptic telescope can correct visual acuity sufficiently for such a person to pass the driver's test, such a unit is not totally practical for use while driving. In fact, a bioptic telescope used while driving is mounted above or below the visual axis of the patient's eye and both head and eye movements away from the center of the visual field are required for the patient to use a bioptic telescope. When the bioptic telescope is mounted directly in the center of the patient's visual axis, there is a blind area surrounding the telescope because the telescope itself blocks a portion of the patient's field of view. A driver wearing such an apparatus ordinarily drives while looking straight ahead through the lens of the eyeglasses. If the driver chooses to use the bioptic telescope mounted above the field of view to read a sign, the head must be tilted downwardly and the eyes turned upwardly to align them with the optical axis of the telescope. In doing so, the central visual field is narrowed from the normal field of about 60.degree. in diameter to a visual field of approximately 6.degree. in diameter. The patient using a bioptic telescope of this construction experiences a significant loss of peripheral visual acuity, and a large blind spot of about 10.degree. width is created surrounding the telescope in the peripheral field of view, a most undesirable result while driving.
Small binocular and monocular telescopes are available from Carl Zeiss, of Oberkochen, West Germany, for mounting on eyeglasses for use as for correcting low vision and for use for microsurgery or other precision work. Those telescopic units can be adapted for mounting on the front of the eyeglasses frame by shortening the tubes and building an extra prismatic lens into the objective lens. Even specially constructed telescopic devices such as a Zeiss system modified in that manner would suffer all of the disadvantages and limitations of traditional bioptic devices. The Zeiss telescope narrows the central visual field, is heavy, and is cosmetically unacceptable to some patients because those telescopes extend from the front of the lens as much as three or four inches.
Galilean telescopes are frequently prescribed, together with a lens cap which includes a lens that can be added to the telescope which is called a reading cap, for viewing objects close to the patient, for patients having various types of retinal damage causing impaired vision. Those telescopes have all of the disadvantages common to bioptic telescope in general, including excessive weight, an unwieldy frontward extension, and the requirement that a patient wearing the device simultaneously tilt the head and rotate the eye to view an image through the device.
Many other bioptic telescopes are known in the art and are prescribed on an individual basis for a patient depending on the patient's specific needs. Binocular telescope systems are prescribed for patients desiring increased visual acuity for reading or close work. Monocular telescope systems can be prescribed for patients having reduced vision in one eye only or for an patient having vision in only one eye.
One available lens system, the "BITA" lens, a product of the Edwards Optical Corp., P.O. Box 3299, Virginia Beach, Va. 23454, is mounted behind the eyeglasses lens directly in front of the eye of the wearer. That system provides magnification, but the lens of the system comes dangerously close to the patient's eye. When the patient blinks, eyelashes invariably brush over the lenses, causing discomfort and irritation within a short period of time.
The disadvantages and difficulties encountered by patients wearing previously available bioptic low vision aids can be overcome by providing a bioptic apparatus which is periscopic rather than telescopic, and thus fits entirely behind the lens of a standard eyeglasses frame in an area to one side of the visual field of the wearer or above or below the normal visual axis of the wearer.
It is, therefore, an object of the present invention to provide a bioptic periscope low vision aid which does not require head movement by a patient wearing and using the apparatus.
Another object of the present invention is to provide a bioptic periscope which requires an eye rotation within a range which is comfortable for use as a low vision aid, i.e., less than about 50 degrees, and which eye rotation can be maintained by the user for extended periods of time if necessary.
Another object of the present invention is to provide a bioptic periscope which can be installed in corrective eyeglasses and which does not create a blind area in the peripheral field surrounding the bioptic apparatus. Such an apparatus does not suffer the disadvantage common to telescopes mounted in front of an eyeglasses lens, which create a magnified central visual field and a blind area surrounding that central visual field.
A further object of the present invention is to provide a bioptic periscope which provides the wearer with a relatively large field of view when in use, up to about 18.degree..
A further object of the present invention is to provide a bioptic periscope which is light enough that the device can be mounted to a standard eyeglasses frame chosen by the wearer rather than being mounted to a specially constructed or heavy duty eyeglasses frame.
A further object of the present invention is to provide a bioptic periscope and simple method of using the apparatus which requires little practice time for a patient to learn to use the apparatus.
Yet another object of the present invention is to provide an apparatus for increasing visual acuity which is cosmetically acceptable to the low vision patient because the apparatus can be concealed behind a standard eyeglasses frame and lens by means of a tinted glass wafer secured over the eyeglasses lens which obscures the view of the apparatus.
Another object of the present invention is to provide a bioptic periscope which can be mounted and used together with either a corrective eyeglasses lens or with a non-corrective eyeglasses lens.
A further object of the present invention is to provide a bioptic periscope and method which can be produced economically and provided to patients at less expense than presently available bioptic low vision aids.
Another object of the present invention is to provide a bioptic periscope which, when mounted behind the eyeglasses lens of a standard eyeglasses frame, permits clearance between the eye piece lens and the eye, eyelid, and eyelashes of the patient.
A further object of the present invention is to provide a bioptic periscope low vision aid which is comfortable for the patient to wear and use.
Yet another object of the present invention is to provide a behind-the-lens bioptic periscope which provides a high quality image with little or no chromatic or optical distortion when used for viewing by the patient.
These and other objects, features, and advantages of the invention will become evident in light of the following detailed description.